[libcxx-commits] [libcxx] [libc++][test] Close LWG3238 and add tests (PR #93043)

[via libcxx-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Hui (huixie90)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/93043.diff


2 Files Affected:

- (modified) libcxx/docs/Status/Cxx20Issues.csv (+1-1) 
- (modified) libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/deduct_F.verify.cpp (+17) 


``````````diff
diff --git a/libcxx/docs/Status/Cxx20Issues.csv b/libcxx/docs/Status/Cxx20Issues.csv
index db57b15256a62..c741ccbcd68e4 100644
--- a/libcxx/docs/Status/Cxx20Issues.csv
+++ b/libcxx/docs/Status/Cxx20Issues.csv
@@ -202,7 +202,7 @@
 "`3226 <https://wg21.link/LWG3226>`__","``zoned_time``\  constructor from ``string_view``\  should accept ``zoned_time<Duration2, TimeZonePtr2>``\ ","Prague","","","|chrono|"
 "`3233 <https://wg21.link/LWG3233>`__","Broken requirements for ``shared_ptr``\  converting constructors","Prague","",""
 "`3237 <https://wg21.link/LWG3237>`__","LWG 3038 and 3190 have inconsistent PRs","Prague","|Complete|","16.0"
-"`3238 <https://wg21.link/LWG3238>`__","Insufficiently-defined behavior of ``std::function``\  deduction guides","Prague","",""
+"`3238 <https://wg21.link/LWG3238>`__","Insufficiently-defined behavior of ``std::function``\  deduction guides","Prague","|Nothing To Do|",""
 "`3242 <https://wg21.link/LWG3242>`__","``std::format``\ : missing rules for ``arg-id``\  in ``width``\  and ``precision``\ ","Prague","|Complete|","14.0","|format|"
 "`3243 <https://wg21.link/LWG3243>`__","``std::format``\  and negative zeroes","Prague","|Complete|","14.0","|format|"
 "`3247 <https://wg21.link/LWG3247>`__","``ranges::iter_move``\  should perform ADL-only lookup of ``iter_move``\ ","Prague","|Complete|","15.0","|ranges|"
diff --git a/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/deduct_F.verify.cpp b/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/deduct_F.verify.cpp
index 8a42d3be3571c..08b0dcfa337dd 100644
--- a/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/deduct_F.verify.cpp
+++ b/libcxx/test/std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.con/deduct_F.verify.cpp
@@ -18,6 +18,7 @@
 // Make sure we stick to the specification.
 
 #include <functional>
+#include <type_traits>
 
 struct R { };
 struct f0 { R operator()() && { return {}; } };
@@ -28,3 +29,19 @@ void f() {
     std::function g = f1{}; // expected-error{{no viable constructor or deduction guide for deduction of template arguments of 'function'}}
     std::function h = nullptr; // expected-error{{no viable constructor or deduction guide for deduction of template arguments of 'function'}}
 }
+
+// LWG 3238. Insufficiently-defined behavior of std::function deduction guides
+// https://cplusplus.github.io/LWG/issue3238
+template <class T, class = void>
+struct IsFunctionDeducible : std::false_type {};
+
+template <class T>
+struct IsFunctionDeducible<T, std::void_t<decltype(std::function(std::declval<T>()))>> : std::true_type {};
+
+struct Deducible {
+    int operator()() const;
+};
+
+static_assert(IsFunctionDeducible<Deducible>::value);
+static_assert(!IsFunctionDeducible<f0>::value);
+static_assert(!IsFunctionDeducible<f1>::value);

``````````

</details>


https://github.com/llvm/llvm-project/pull/93043